@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

#bookstack-side-button,
window:not([active="true"]) #bookstack-side-button,
toolbar[iconsize="small"] #bookstack-side-button {
  list-style-image: url("chrome://bookstack-os/skin/bookstack-button.png");
}
#bookstack-side-button > .toolbarbutton-icon {
  margin: 0px !important;
  width: auto !important;
  height: auto !important;
}
